Grebe

Grebes (/ˈɡriːbz/) are aquatic diving birds in the order Podicipediformes (/ˌpɒdɪsɪˈpɛdɪfɔːrmiːz/). Grebes are widely distributed freshwater birds, with some species also found in marine habitats during migration and winter. Most grebes fly, although some flightless species exist, most notably in stable lakes. The order contains a single family, the Podicipedidae, which includes 22 species in six extant genera.

Although, superficially, they resemble other diving birds such as loons and coots, they are most closely related to flamingos, as supported by morphological, molecular and paleontological data. Many species are monogamous and are known for their courtship displays, with the pair performing synchronized dances across the water's surface. The birds build floating vegetative nests where they lay several eggs. About a third of the world's grebes are listed at various levels of conservation concerns—the biggest threats including habitat loss, the introduction of invasive predatory fish and human poaching. As such, three species have gone extinct.

The word "grebe" comes from the French grèbe, which is of unknown origin and dates to 1766. It is possibly from the Breton "krib" meaning 'comb', this referring to the crests of many of the European species. However, grèbe was used to refer to gulls. The appearance of "grebe" in the English language was introduced in 1768 by the Welsh naturalist Thomas Pennant when he adopted the word for the family. Some of the smaller species are often referred to as "dabchick", which originated in the mid-16th century in English, as they were said to be chick-like birds that dive. The clade names "Podicipediformes" and "Podicipedidae" are based on the genus Podiceps which is a combination of Latin of podex, gen. podicis ("rear-end" or "anus") and pes ("foot"), a reference to the placement of a grebe's legs towards the rear of its body.

Grebes are small to medium-large in size ranging from the least grebe (Tachybaptus dominicus), at 120 g (4.2 oz) and 23.5 cm (9.3 in), to the great grebe (Podiceps major), at 1.7 kg (3.7 lb) and 71 cm (28 in). Despite these size differences, grebes are a homogeneous family of waterbirds with very few or slight differences among the genera.

On the surface of the water, they swim low with just the head and neck exposed. All species have lobed toes and are excellent swimmers and divers. The feet are always large, with broad lobes on the toes and small webs connecting the front three toes. The hind toe also has a small lobe. The claws are similar to nails and are flat. These lobate feet act as an oar, as when moving forward, they provide minimum resistance, and moving backwards, they provide maximum coverage.

The leg bones (femur and tarsometatarsus) are equal in length, with the femur having a large head and the presence of long cnemial crests in the tarsometatarsus. The patella is separate and supports the tarsometatarsus posteriorly, which greatly helps with the contraction of the muscles. They swim by simultaneously spreading out the feet and bringing them inward, with the webbing expanded to produce the forward thrust in much the same way as frogs. However, due to the anatomy of the legs, grebes are not as mobile on land as they are on the water. Although they can run for a short distance, they are prone to falling over, since they have their feet placed far back on the body.

The wing shape varies depending on the species, ranging from moderately long to incredibly short and rounded in shape. The wing anatomy in grebes has a relatively short and thin carpometacarpus-phalanges component, which supports their primary feathers, while the ulna is long and fairly weak, supporting secondary feathers. There are 11 primaries and 17 to 22 secondaries, with the inner secondaries being longer than the primaries. As such, grebes are generally not strong or rapid fliers. Some species are reluctant to fly. Indeed, several have become flightless. In these flightless species, they tend to have a reduction in the length of their wings, tails, and primaries; reduced pectoral muscles, and a significant increase in body size. Since grebes generally dive more than fly, the sternum can be as small or even smaller than the pelvic girdle. When they do fly, they often launch themselves off from the water and must run along the surface as they flap their wings to provide a lift.

Bills vary from short and thick to long and pointed, depending on the diet, and are slightly larger in males than in females (though the sizes can overlap between younger males and females).